Adjustable coupling device



Sept. 20, 1949. A. E. DOWELL, m 2,432,471

ADJUSTABLE COUPLING DEVICE Filed April 15, 1948 Load WITN ESSESI 4 INVENTOR inf/7 ur EDowg/l E,

ATTORNEY rmmds t'zo, 1949 ADJUSTABLE COUPLING DEVICE Arthur E. Dowel], m. Washington. n.'c.', assignor to Westinghouse Electric Corporation. East Pittsburgh, Pa., a corporation of Pennsylvania Application April 1:, ms, Serial No. cases My invention relates to adjustable coupling devices'for radio circuits and in particular relates to a combined transformer and inductor coil ior coupling the output circuit of a balanced mixer with the input of a push-pull amplifier.

So-called balanced-mixer circuits are employed in the radio art where a carrier frequency and a modulated frequency are being impressed on the grids of a mixer tube in order to produce an output having carrier frequency modulated in accordance with an input signal or the like. In one convenient form of the circuit for this purpose, a pair of multi-grid tubes are used, the carrier frequency being impressed on the grids of the two tubes in parallel and the modulating frequency being impressed on the other pair of grids in push-pull. when this is done, the carrier frequency will cancel itself out if the output circuits of the'two tubes are likewise arranged in pushpull, so that only the two side-band frequencies are impressed on a load circuit energized therefrom. The undesired side band can then be substantially suppressed in the load circuit by tuning the latter to the desired side band. One convenient way of arranging the output circuits of such a pair of tubes is to provide an inductive winding in series with the anode of each of the above-mentioned push-pull tubes which acts as the primary winding of a transformer, this primary winding being in inductive relation to a secondary winding which is connected to the grids of a push-pull amplifier.

One object of my invention is accordingly to provide a convenient structure embodying the two primary windings and secondary windings above mentioned.

Another object of my invention is to provide a structure embodying the two primary windings and secondary windings above mentioned with a pair of magnetic cores, such that the inductive eflect of the two primary windings on the secondary winding can be accurately balanced windings on the secondary winding, and the selfinductance of the secondary winding, may be varied independently of each other.

2 Claims. (CL 171-419) Other objects of my invention will become apparent on reading the following description taken in connection with the drawing, in which:

Figure 1 is a schematic diagram of a balanced mixer and amplifier circuit embodying a trans- !ordmer made in accordance with my invention; an

Fig. 2 is a diagrammatic showing of a longitunected to the opposite ends of the secondary windings 4 and 5 of a push-pull input transformer which derives modulating frequency voltage from a primary winding 8. The plate circuits of the tubes I and 2 are respectively connected to the opposite terminals of a pair of primary windings I and I, which are connected to oppose each other in magnetic eflect on a secondary winding 9. The adjacent terminals of the windings I and t are connected together to the positive terminal B+ of a direct-current voltage source (not shown) having its negative terminal connected through the ground to the two cathodes of the tubes i and 2. The terminals of the secondary winding 9 are shunted by a variable capacitor ii and are respectively connected to the control grids of a pair of push-pull amplifier tubes i2 and i3 connected to suppl energy in push-pull to a load II. The cathodes of the tubes l2 and I3 are connected through ground to the midpoint of the secondary winding 8.

The windings I, 8 and 9 above describedmay be mounted, in accordance with my invention on a cylinder ll of insulating material as shown in detail in Fig. 2. The cylinder 2| is preferably enclosed in an aluminum casing 22 having at one end a terminal board of insulating material supporting connection-terminals 23 to 28, inclusive, by which the windings I, 8 and 9 may be connected into the circuit, as is shown in Fig. 1. The cylinder 2i may conveniently be held in place in the casing 22 by gripping a portion of the latter between a shoulder 29 on the cylinder 2i and a nut 3| making threaded engagement with the outer end of the cylinder 2 I.

In the hollow interior of the cylinder 2| there projects a second cylindrical member 32 which may be of suitable insulating material and which is supported coaxially with the cylinder It by making threaded engagement with the end portion thereof near the shoulder 88. The cylindrical member 82 is slightly smaller than the cylindrical member 2| so that it can be moved longitudinally thereof by the action of its threaded engagement therewith when it is turned about the common axis by any suitable tool applied to its projecting end. The cylindrical member 82 is hollow and has fastened inside its end remote from its threaded engagement with cylinder 2| a core 88 of powdered magnetite or other suitable magnetic material. The winding 8 is positioned on the outside of the cylinder 2| in a position which is symmetrical relative to the ends of said magnetic core 88.

Separated from the magnetic core 88 within the cylinder 82 is a second core 84 of some similar magnetic material which is of such diameter as to slide readily along the axis of the cylinder 8!. A screw 85 threaded into the end of the cylindrical member 82 ensages the core 88 and may conveniently be used to displace the core 88 axially along the cylindrical member 88 for regulating purposes which will be described below.

The winding 8 is positioned on the exterior of the cylindrical member 21 in"such a position that the cores 88 and 88 'are somewhat displaced laterally from its opposite faces, and the windings i and 8 are symmetrically placed relative to the winding 8. The core 88 is then given a preliminary adjustment to a position in which its ends project in opposite directions from the opposed end-faces of the winding I.-

As shown in Fig. 2, the similar terminals of the windings 1 and 8 are connected to the terminal stud 28 which is adapted to be connected to the battery terminal 3+ in Fig. 1. The other ends of the windings I and 8 are-respectively connected to the terminal pins 28 and 28 on the terminal board from which they may be respectively connected to the anodes of the tubes l and I in Fig. 1. An intermediate point on the winding 8 is connected to the terminal stud-21 from which it is adapted to be connected to ground, as shown in Fig. 1. The opposite ends of the winding 8 are then respectively connected to the terminal studs 24 and 28 from which connections may be made to the grids of the amplifier tubes i2 nd I8 shown in Fig. 1.

It will be observed that by turning the screw 88, the air gap between the magnetic cores 88 and 84 may be varied at will, thus varying the amount of magnetic coupling between the coils 1 and 8 on the one hand and the secondary winding 8 on the other. Such a variation of the position of the cores 88 and 84 varies the leakage inductance of the winding 8 and makes it possible to thereby assist in tuning the frequency of the resonant circuit comprising winding 8 and capacitor II. On the other hand by turning the cylindrical member 88 relative to the cylinder 8|,

v 4 thecores88and8lmaybedisplsoedalongthe common axis of the two cylinders, thereby increasing the inductive elect on the seeimdary windinglofoneoftheprimarywindinss'landl. The structure I have described therefore maku itpossibletoaddustthecouplingofthewindings I and8tothewinding8insuchawayasmnbe required to cause the inductive effecil of tlie carrier frequency current flowing in the windingsland8toneutra1ineinthewinding8;and at the same time to vary the leakage inductance of the winding 8 to tune itwiththe capacitor II to a desired side-band frequency.

1 claim as my invention:

1.-.A variable transformer comprising a secondary winding supported on an insulating frame. apairofprimarywindingsspacedapartfrcm said secondary winding on opposite sides thereof on said frame, a support member for a pair of magnetic cores within said frame, one of said cores being amxed to said support member and positioned within one of said primary windings, the other of said cores being slidable along said support member in anaxial direction in a region adjacent to the other of said primary windings. means to variably displace said support member axially with respect to said frame and means to displace said slidable core member relative to said support member.

2. A radio transformer comprising an insulating hollow cylinder supporting on its exterml surface a secondary winding and a pair of similar primary windings displaced axially of said cylinder from opposite faces of said primary winding, a cylindrical member of insulating material coaxial with the first mentioned cylinder and making threaded engagement for displacement along the axis thereof, a first magnetic core aiiixed to said cylindrical member and aligned with one of said primary windings, a second magnetic core slidable within said cylindrical member in a region adjacent said other primary winding, and means making threaded engagement with said cylindrical member for displacing said second magnetic member axially of said cylindrical member.

ARTHUR I. DOWILL, m.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 55 2,132,875 Myers Oct. 11, 1888 2,346,584 Jacob Apr. 11. 1844 2,430,757 Conrad et al Nov. 11, 194'! FOREIGN PATENTS 5 Number Country Date 295,955 Great Britain June 28, 1828 

